Copper and copper alloys are often substituted for the more traditional aluminum and aluminum alloys as the primary signal and power carrying conductive structures in integrated circuits. Unfortunately, when copper and copper alloy pads are wire-bonded to a highly conductive wire, such as a gold, using current state-of-the-art wire-bonding processes, the resulting copper and gold bonds or copper alloy and gold bonds are not as reliable as aluminum and gold bonds or aluminum alloy and gold bonds used in the prior art.
One solution to this problem is shown in the prior art bonding structure 100 of FIG. 1. Bonding structure 100 includes substrate 103, copper conductor 106, dielectric layer 109, barrier layer 112, aluminum layer 115, passivation layer 116 and polyimide layer 118. To avoid wire-bonding to copper, dielectric layer 109 is etched at the location of copper conductor 106, and a barrier layer 112 of titanium or titanium nitride is deposited above copper conductor 106. Aluminum layer 115 is deposited above barrier layer 112, and passivation 116 and polyimide layers 118 are deposited above aluminum layer 115. Finally, passivation 116 and polyimide 118 layers are etched to expose aluminum layer 115 for wire-bonding. Unfortunately, this solution has several problems. First, it requires two extra masking operations that are not required when wire-bonding to an aluminum or an aluminum-copper conductor. It requires a masking operation to expose copper conductor 106 prior to depositing barrier layer 112 and aluminum layer 115, and it requires a masking operation to pattern aluminum layer 115, prior to wire-bonding. Second, the extra processing steps increase the complexity of the manufacturing operation and the failure rate of the manufactured circuits. Third, the solution is expensive, since it requires more materials, masking steps, and time than the prior art processes to manufacture the integrated circuit.
For these and other reasons there is a need for the present invention.